The Internet of Things (“IoT”) is the network of physical devices, vehicles, buildings, and other items embedded with electronics, software, sensors, actuators, and network connectivity that enable these objects to collect and exchange data. The deployment of IoT relies on networks of low-cost wireless devices that reliably work in the presence of interference. However, such low-cost wireless devices are sensitive to carrier frequency offset (“CFO”) between the transmitter and receiver, especially under circumstances where there is a low signal-to-noise ratio (“SNR”). CFO often occurs when the local oscillator signal for down-conversion in the receiver does not synchronise with the carrier signal contained in the received signal. This phenomenon can be attributed to two factors: frequency mismatch in the transmitter and the receiver oscillators, and the Doppler effect as the transmitter or the receiver is moving. When this occurs, the received signal will be shifted in frequency.
For an OFDM system, the orthogonality among sub-carriers is maintained only if the receiver uses a local oscillation signal that is synchronous with the carrier signal contained in the received signal. Otherwise, a mismatch in carrier frequency can result in inter-carrier interference (“ICI”). The oscillators in the transmitter and the receiver will most likely never be oscillating at an identical frequency. Therefore, a carrier frequency offset almost always exists even if there is no Doppler effect.
As a result, especially under the circumstances of such wireless communications where there is a low SNR, it is important that the receiver produce an adequate CFO estimation to compensate for the CFO. Poor CFO estimation results in poor demodulator performance in the presence of crystal frequency mismatches between various nodes in such a wireless communication network. Various frequency offset estimation techniques have been developed to correct for CFO in the receiver. However, the various techniques can be complex and expensive in terms of hardware, memory usage, and/or the power requirements of the device in which the receiver is implemented.
A particular type of wireless communication network where it is important to perform CFO estimation in devices that need to be implemented at a low cost and at low-power requirements is Bluetooth® Low Energy (“BLE”), including BLE Long-Range (“BLE-LR”). More details about BLE can be found within the Bluetooth® v5.0 Specification, which is hereby incorporated by reference herein.